After being lost in space for months, your spacecraft just landed on what
looks like a desert on Earth.  Could you have been lucky enough to really
have landed on your home planet?  As you walk around on the surface, you
notice that, after many months of weightlessness, gravity feels very
different than it used to feel on Earth.  Is gravity really different here
or has the long trip affected you?

You unpack your bathroom scale and you find that your weight has really
changed considerably.  Was it the food on the spacecraft...?  Or perhaps,
your weight has changed but your mass hasn't.  Gravity is just different
here.  This may not be Earth after all!

The best way to find out whether or not you're on Earth is with a pendulum
and a stop watch.  Carefully measure the length and the period and use the
pendulum formula to find g.  Remember that this simple formula is only
accurate for small oscillation amplitudes.  Repeat your measurements until
you get consistent results.  If you need instructions on how to make these
measurements, go back to   PRACTICE    and read that "help" screen. 

The batteries in your watch are almost dead and you must build an old 
fashioned clock using another pendulum to keep track of time. Based on
your previous result, how long must this pendulum be to have a period of 
one second.  Check your calculations and press F2 to enter your answers.